Columbium base alloy



United rates This invention relates to a columbium base alloy containing titanium, iron and chromium as the major alloying ingredients.

The development of rockets and missiles and advances in nuclear reactors and gas turbines necessitate the use of materials of construction under extreme conditions of temperature and operation. It is necessary under these conditions to have superior alloys which combine workability, high-temperature strength and high-temperature oxidation resistance in an alloy.

Accordingly, it is an object of the present invention to provide an alloy which is characterized by resistance to high-temperature oxidation even at temperatures in excess of 1100 C.

It is another object of the present invention to provide an alloy which is amenable to heat treatment by conventional means.

Still another object of the present invention is to provide an alloy which, when exposed to an oxidizing atmosphere at elevated temperatures, forms a pellicular metal oxide which adheres firmly to the alloy and is not substantially volatilized therefrom.

Other objects will be apparent from the subsequent disclosure and appended claims.

The alloy which satisfies the objects of the present invention consists essentially of from 1 to 40 weight percent of titanium, 8 to 30 weight percent iron, 3 to 35 weight percent chromium, up to 10 weight percent vanadium, up to 30 Weight percent tungsten, up to 30 weight percent tantalum, the aggregate of said vanadium, tungsten and tantalum not exceeding 50 weight percent, up to 20 weight percent in the aggregate of at least one metal selected from the group consisting of nickel and cobalt, up to 5 weight percent in the aggregate of at least one alloying element selected from the group consisting of barium, silicon, beryllium, yttrium, boron and the rare earth metals, the remainder being columbium in a minimum amount of at least 30 weight percent.

While the foregoing alloy satisfies all of the objects set forth above, it has been found that an alloy consisting essentially of from 1 to 30 weight percent titanium, 8 to 25 weight percent iron, 3 to 35 weight percent chromium, up to 10 weight percent vanadium, up to 20 weight percent tungsten, up to 20 weight percent tantalum, the aggregate of said vanadium, tungsten and tantalum not exceeding 40 weight percent, up to 15 weight percent in the aggregate of at least one metal selected from the group consisting of nickel and cobalt, up to 5 weight percent in the aggregate of at least one alloying element selected from the group consisting of barium, silicon, beryllium, yttrium, boron and the rare earth metals, the remainder being columbium in a minimum amount of at least 35 weight percent is particularly outstanding for use under oxidizing conditions and particularly hi gh-temperature oxidizing conditions since the alloy strongly resists reaction with oxygen at temperatures in excess of 1100 C.

The maximum benefits of the present alloy are obtained when the alloy consists essentially of from to 20 weight percent titanium, 15 to 25 weight percent iron, 5 to 30 weight percent chromium, 0 to weight percent vanadium, 0 to 20 weight percent tungsten, 0 to 20 weight percent tantalum, the aggregate of said vanadium, tungsten and tantalum not exceeding 30 weight percent, up to 3,037,358 Patented June 5, 1952 weight percent in the aggregate of at least one metal se lected from the group consisting of nickel and cobalt, up to 3 weight percent in the aggregate of at least one alloying element selected from the group consisting of barium, silicon, beryllium, yttrium, boron and the rare earth metals, the remainder being columbium in a minimum amount of at least 40 weight percent.

The alloys of the present invention may be prepared by any number of methods such as the conventional methods using inert operating conditions, e.-g., by the consumable arc-melting technique described in US. Patent No. 2,640,860, by non-consumable arc melting, by pressing and sintering of metallic powders, or by other powder metallurgical processes. Great caution should be exercised to protect the metals from the atomsphere since contamination of the alloying mass by nitrogen and oxygen, etc. destroys many of the valuable properties of the alloy. To protect the alloying materials from these atmospheric contaminants the alloying operation should be performed under vacuum or in an inert atmosphere, such as argon or helium, or under a protective slag or under a combination of protective slag and controlled atmosphere. The final shaping of the alloy metal may be accomplished after cooling by any of the several procedures, such as, extrusion, swaging, rolling, or grinding the cast or sintered shape.

The example provided below were prepared in a nonconsurnable arc furnace such as that described by W. Kroll in Transactions of the Electro-Chernical Society, volume 78, 1940, pages 35 through 47. The procedure consists of placing the component metals on a water cooled, copper crucible shaped to retain the charge in a hearth like depression and incorporated in a gas tight container supplied with a tungsten electrode capable of impressing an arc onto the charge. After careful evacuation of the system the charge was melted four times under an argon atmosphere until a homogeneous alloy of the desired composition was obtained.

The oxidation resistance of the alloy was determined by exposing highly polished specimen measuring approximately 1.60 x 0.85 x 0.65 centimeters to a stream of pure, dry oxygen within an air tight container. The specimens were suspended and heated in this atmosphere at 800 C., 1000 C. or 1200 C. and the amount of pellicular metal oxide formed on the surfaces during the exposure was continuously measured and recorded automatically by means of balances of the Manor type. By this method an accurate rate of oxidation weight gain could be obtained for the alloys tested. The weight gain is expressed in milligrams of weight gained per square centimeter of surface exposed for at least hours at the difierent temperatures.

EXAMPLE I A homogeneous melt containing 35 percent columbium, 25 percent titanium, 20 percent iron, 15 percent chromium, and 5 percent tantalum was prepared by melting the above-cited elemental metals together in the manner described previously and the alloy so prepared was tested for its oxidation resistance. Under these conditions, the alloy showed a 100 hour weight gain of 3.02 milligrams per square centimeter at 800 C., 20.4 milligrams per square centimeter at 1000 C., and 96.8 milligrams per square centimeter at 1200 C. Unalloyed columbium shows weight gains of 3630 milligrams per square centimeter at 800 C., 6 670 milligrams per square centimeter at 1000 C., and 24,000 milligrams per square centimeter at 1200 C. under identical testing conditions.

EXAMPLE -II Adopting the procedures used in Example I, an alloy was prepared containing 40 percent columbium, 25 percent 3 titanium, 20 percent iron, and 15 percent chromium. Upon testing for its oxidation resistance, the 100 hour weight gain, expressed in milligrams per square centimeter, was found to be 6.55 at 800 C., 16 at 1000 C., and 77.4 at 1200" c. v

EXAMPLE III Adopting the procedures used in Example I, an alloy was prepared containing 45 percent columbium, 25 percent titanium, 20 percent iron, and 10 percent chromium. Upon testing for its oxidation resistance, the 100 hour weight gain, expressed in milligrams per square centimeter, was found to be 8.56 at 800 C., 20.4 at 1000 C., and 68.5 at 1200 C.

Adopting the procedures used in Example I, an alloy was prepared containing 49 percent columbium, 20 percent iron, 15 percent titanium, 15 percent chromium, and 1 percent barium. Upon testing for its oxidation resistance, the 100 hour weight gain, expressed in milligrams per square centimeter, was found to be 3.82 at 800 C., 14.1 at 1000 C. and 31.6 at 1200 C.

In addition to the ranges of alloy compositions described previously. certain specific compositions have been found to have exceptional properties. These compositions are shown in Table I.

Table l ALLOY COMPOSITION Percent Cb 60 54. 5 35 Percent Ti 10 25 Percent Fe. 20 20 20 Percent 01' 10 15 Percent Be, Be, Si and/or rare earth metals .5 Percent Ta 5 Although it is preferable to use high-purity metals in the preparation of the alloys of the present invention, a small amount of variance in purity can be tolerated before product quality suffers appreciably. The alloys of the working examples are prepared from commercially cidental impurities.

In the present disclosure and appended claims, the phrase up to shall be construed to include zero as the lower limit of the percentage range of optional elements recited.

What is claimed is:

1. An alloy consisting essentially of from 5 to 20 weight percent titanium, 15 to 25 weight percent iron, 5 to weight percent chromium, up to 10 weight percent vanadium up to 20 weight percent tungsten, up to 20 weight percent tantalum, the aggregate of said vanadium, tungsten and tantalum not exceeding 30 weight percent, up to 15 weight percent in the aggregate of at least one metal selected from the group consisting of nickel and cobalt, up to 3 weight percent in the aggregate of at least one alloying element selected from the group consisting of barium, silicon, beryllium, yttrium, boron and the rare earth metals, the remainder being columbium in a minimum amount of at least weight percent.

2. An alloy consisting essentially of about 10 weight percent titanium, about 20 weight percent iron, about 10 weight percent chromium, the balance being columbium and incidental impurities.

3. An alloy consisting essentially of about 10 weight percent titanium, about 20 weight percent iron, about 15 Weight percent chromium, about .5 weight percent in the aggregate of at least one member selected from the group consisting of barium, beryllium, silicon and the rare earth metals, the balance being columbium and incidental impurities.

4. An alloy con isting essentially of about 25 weight percent titanium, about 20 weight percent iron, about 15 weight percent chromium, about 5 Weight percent tantalum, the balance being columbium and incidental impurities.

References Cited in the file of this patent UNITED STATES PATENTS 1,588,518 Brace June 15, 1926 1,701,299 Engle Feb. 5, 1929 2,187,630 Schafer Jan. 16, 1940 2,822,268 Hix Feb. 4, 1958 2,838,395 Rhodin June 10, 1958 2,882,146 Rhodin Apr. 14, 1959 2,883,282 Wainer Apr. 21, 1959 FOREIGN PATENTS 718,822 Germany Mar. 24, 1942 

3. AN ALLOY CONSISTING ESSENTIALLY OF ABOUT 10 WEIGHT PERCENT TITANIUM, ABOUT 20 WEIGHT PERCENT IRON, ABOUT 15 WEIGHT PERCENT CHROMIUM, ABOUT .5 WEIGHT PERCENT IN THE AGGREGATE OF AT LEAST ONE MEMBER SELECTED FROM THE GROUP CONSISTING OF BARIUM, BERYLLIUM, SILICON AND THE RARE EARTH METALS, THE BALANCE BEING COLUMBIUM AND INCIDENTAL IMPURITIES. 